AArch64 ESR Trapped WFI 或 WFE 指令执行

Question

I am confused by the following entry in the ARM documentation for ESR_EL1:

EC, bits [31:26] 0b000001 Trapped WFI or WFE instruction execution.

What does it really mean that WFI or WFE were trapped? What is the meaning if this happens under Linux? Could this produce a kernel crash?

Answer 1

It means that SCTLR_EL1.nTWI (bit 16) or SCTLR_EL1.nTWE (bit 18) were set to 0 , and something running at EL0 executed a WFI or WFE instruction.

Linux AArch64 userspace was apparently allowed to execute WFI / WFE until this patch , which installed an exception handler in the kernel that would skip the instructions, effectively turning them into NOP s.